feat: support Octets for Char/Varchar

[KKould]

What problem does this PR solve?

create table t1(id int primary key, v1 char, v2 char(5 characters), v3 char(5 octets))

insert into t1 values(0, '🖕', '🖕🖕🖕🖕🖕', '🖕');

insert into t1 values(1, null, null, null);

select * from t1;
----
0 🖕 🖕🖕🖕🖕🖕 🖕
1 null null null

Tips: originally, LogicalType::Char/LogicalType::Varchar could get the exact value in the LogicalType::raw_len method, but now only Octet's Char/Varchar is allowed to be returned, because only Octet determines the number of Bytes, while Character only limits the number of characters. In utf8, The minimum number of bytes of 4 characters is 4 and the maximum is 16(undetermined number of bytes)

What is changed and how it works?

Code changes

• Has Rust code change
• Has CI related scripts change

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Note for reviewer